Immunoglobulin A (IgA) is the predominant immunoglobulin on human mucosal surfaces. IgA has antibody activity against a wide range of bacteria, viruses, toxins and enzymes. In the human oral cavity, this activity is diminished by the presence of an IgA- specifc protease secreted by Streptococcus sanguis, a micro- organism prominent in dental plaque. The specific aims of this proposal are: 1) to characterize the IgA protease produced; 2) to determine the mechanisms by which Actinomyces viscosus (a periodontal pathogen found in close association with S. sanguis) accelerates the course of IgA protease secretion when growth in co-culture with the streptococcus; 3) to isolate and characterize the substances in human saliva which stabilize the IgA protease against thermal and proteolytic denaturation; 4) to compare IgA protease production in hyperproducer strains and wild type strains of S. sanguis. The long-term objectives of this research are: 1) to develop a chemically defined system for IgA protease production which will facilitate purification of the enzyme by providing higher initial specific activity, increase the resolution of immunochemical studies by elimination of cross-reactive media constituents, and allow comparison of higher production of the enzyme by hyperproducing strains and stabilization of the enzyme against thermal and proteolytic denaturation so as to provide sufficient quantities on which to perform enzyme characterization and amino acid sequencing studies.